Creation of a Simple DLL

Introduction

This article shows a step-by-step technique to create your first DLL with VC++.

Steps to Create Your First DLL

• Create a Win32 Dynamic Link Library project, adding a *.cpp and a *.h file.
• In the *.cpp file, create a class instantiated from the CWinApp file.
  C++

  # include <stdafx.h>
  # include "SourceFile.h"
  
  class CDllApp : public CWinApp
  {
      public:
    
          CDllApp::CDllApp()
          {
              Calc(0,0);
          }
  
          DECLARE_MESSAGE_MAP()
  };
  
  BEGIN_MESSAGE_MAP(CDllApp,CWinApp)
  
  END_MESSAGE_MAP()
  
  CDllApp DllObject;

• In the *.h file (here it is SourceFile.h), define the functions to be used. Also specify the dllexport value for the _declspec function.
  C++

  extern "C" _declspec(dllexport) int Calc(char no1,char no2)
  {
      char result;
      result = no1 + no2;
      return result;
  }

• Then compile the DLL.
• Create a normal Win32 Application with a *.cpp file and a *.h file.
• In the *.h file, (here it is AppHeader.h ), declare the function with the dllimport value of _declspec.
  C++

  extern "C" _declspec(dllimport) Calc(int FirstValue,
      int SecondValue);
  

• In the *.cpp file, use the function.
  C++

  # include "AFXWIN.H"
  # include "AppHeader.h"
  
  class MainFrame : public CFrameWnd
  {
      public:
  
          MainFrame()
          {
              Create(0,"Trial");
          }
  
          void OnLButtonDown(UINT nFlags,CPoint point)
          {
              int res;
              char str[5];
              res = Calc(998,226);
              sprintf(str,"%d",res);
              MessageBox(str);
           }
  
           DECLARE_MESSAGE_MAP()
  };

• In the Link tab of the "Project->Settings" dialog, go to the text box labeled "Object / Library Modules" and specify the path of the DLL file. Then copy the compiled DLL file to your current appliation path directory and run the program.

Some Things to Note

The DLL file may not be visible due to the File View options in the Windows folder. So, you can either go to the DOS prompt and copy the file or enable the setting "Show all files" in Windows Explorer to copy the file. To create a DLL that uses MFC, see the following example. Note that extern "C" has not been used and the macro AFX_MANAGE_STATE(AfxGetStaticModuleState()); has been used to implement MFC.

 _declspec(dllexport)CString Display(CString a,CString b)
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());
    CString Str;
    Str = a + b;
    return Str;
}

That's all, folks. All luck and have a great time.